Generally various inorganic fillers are added to high molecular weight polymers for reinforcement thereof. Those filler-containing polymers are used as materials for various parts for semiconductor production apparatuses which require a clean environment.
Recently a highly clean environment has been demanded in production of semiconductors in proportion to high performance of semiconductors. As a result, it is required not only to eliminate only micro-particles but also to minimize gaseous impurities generated in semiconductor production processes (generally called “impurity outgas”).
Such impurity outgases encompass moisture and organic gases such as dioctyl phthalate (DOP). Firstly reduction of an amount of outgas generated from a high molecular weight polymer has been aimed at.
Further in consideration of necessity of highly cleaning a filler contained in a high molecular weight polymer material in relatively much amount, there was developed a method of firstly carrying out specific cleaning of the filler and then treating a surface of the filler with a silane coupling agent or the like to reduce an amount of hydroxyl around the surface of the filler, thereby reducing an amount of moisture generation.
However in that method, though generation of moisture outgas can be reduced considerably, generation of organic outgas is not decreased but is increased. Therefore further improvements are required.
The present inventors have found that in the treatment for cleaning of a filler, when the filler is heated in an inert gas stream after making a surface of the filler hydrophobic, generation of not only moisture outgas but also organic outgas can be reduced, and thus have completed the present invention.